Method of apportioning liquid metal in an electromagnetic conveyor trough

ABSTRACT

In the delivery of liquid metal in an electromagnetic conveyor trough from a bath, e.g., a melting vessel or a hot holding vessel, there is a difficulty in reconciling the propelling of liquid metal along the trough and the intermittent delivery of metal in predetermined quantities, and this difficulty is overcome according to the invention by controlling the energy density in that part of the coil which regulates the propelling of the liquid metal in the trough so that it is exclusively determined by the energy density in that part of the coil which regulates the delivery of the liquid density, namely that it is from 10 percent to 30 percent higher than the said delivery current density. By this means the pouring rate of the liquid becomes independent of the level of metal in the said liquid metal bath.

United States Patent [1 3,612,720

[72] Inventor Axel von Stanck 3,045,599 7/1962 Carlson 417/50 Remscheid-Luttringhausen, Germany 3,113,042 12/1963 Hall 198/41 [21] App]. No. 821,479 3,052,097 9/1962 Tymer 60/52 5253 :83 Primary Examiner-William L. Freeh [73] Assignee MiG-Em Gmb A orney Cushman, Darby & Cushman Remscheid-Hasten, Germany [32] Priority Oct. 1, 1968 [33] Germany [31] P 18 00 124.6

I ABSTRACT: In the delivery of liquid metal in an electromag- [54] METHOD OF APPORTIONING LIQUID METAL IN netic conveyor trough from a bath, e.g., a melting vessel 01' a AN ELECTROMAGNETIC CONVEYOR TROUGH hot holding vessel, there is a difficulty in reconc ling the propelling of liquid metal along the trough and the intermit- 2 Claims, 1 Drawing Fig.

tent delivery of metal in predetermined quantities, and this [52] US. Cl 417/50, m n is overcome according to the invention by com 222/70 trolling the energy density in that part of the coil which regu- [51] Int. Cl F04b 19/04 kites the propemng f he liquid metal in the trough so that it is [50] Field of Search 417/50; exdusivdy determined by the energy density in that part of 266/38il98/41i227/70 the coil which regulates the delivery of the liquid density, namely that it is from 10 percent to 30 percent higher than the [56] References cued. said delivery current density. By this means the pouring rate of UNHED STATES PATENTS the liquid becomes independent of the level of metal in the 2,865,291 12/1958 Watt 417/50 said liquid metal bath.

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imam 19 PATENTEDUBT 12 m INVENTOR. AX EL VON STA RCK Y//JAHM u", (of! $11M! ATTORNEY METHOD OF APPORTIONING LIQUID METAL IN AN ELECTROMAGNETIC CONVEYOR 'l'ROUGl-l This invention relates to the apportioning of liquid metal in an electromagnetic conveyor trough, and particularly relates to improving the accuracy with which said delivery is controlled.

A known method of delivering liquid metal in predetermined portions from a melting or a hot holding vessel to casting moulds, consists in propelling it up a rising electromagnetic conveyor trough. It has been suggested that predetermined portions of the liquid metal may be deliveredinto casting moulds by keeping the major part of the induction coil of the conveyor trough adjacent the holding or melting vessel permanently at the appropriate voltage for continuously propelling the melt up the trough, whereas the part of the induction coil at the delivery end of the trough is energized only for the time pouring proceeds. In this suggested method it is assumed that the energy densities applied to the conveyed volume of metal per unit of time, i.e. by the part of the coil associated with the propelling part of the trough and the part of the coil for delivery of the metal, are always the same.

However it transpires in practice that when the energy densities of the inductor coil in the propelling and delivery parts of the conveyor trough are the same, the accuracy of delivery is not very great. This is due to the fact that during the intervals between pouring the propelling action on the liquid metal and the return flow of metal into the propelling part of the trough are superimposed, and that as a result the depth of liquid metal contained in the propelling part of the trough is not unifonn but decreases from the furnace end towards the pouring spout, end of the trough. This decrease is caused by the fact that not all the propelled liquid metal reaches the holding point in the upper half of the trough before beginning to flow back, but that part begins to reverse its direction of flow sooner. The resulting wedge-shaped configuration of the layer of metal in the trough is extended into the delivery part of the trough when this is reactivated by the reenergization of this part of the induction coil, and the electrical energy applied to the inductor is such that the energy density of the propelling part of the induction coil is less than that of the delivery part of the induction coil. As a consequence the pouring rate will then depend upon the level of the liquid metal bath in the melting or hot holding vessel. The same phenomenon occurs when the energy density in an induction coil in the propelling and in the delivery section, are equal. This is naturally undesirable because it is the aim to pour like portions of metal irrespectively of the level of the bath.

Another factor which operates to vary the accuracy of delivery by the conveyor trough derives from fluctuations of the voltage applied to the inductor.

It is the object of the present invention to provide a method of improving the accuracy with which prescribed portions of liquid metal are delivered by an electromagnetic conveyor trough, and to this end the invention consists in using an energy density for the part of the induction coil associated with the propelling part of the electromagnetic conveyor trough of from to percent higher than that used for the part of the induction coil associated with the delivery part of the electromagnetic conveyor trough.

This feature of raising the energy density of the part of the induction coil associated with the propelling part of the electromagnetic conveyor trough results in the pouring rate of the liquid metal becoming independent of the level of the metal in the aforesaid liquid metal bath, due to the fact that it is exclusively determined by the energy density of the part of the inductor coil associated with the apportioning part of the trough. simultaneous forward flow and return flow of the liquid metal being absent. Moreoverthe increase in the energy density of the part of the induction coil associated with the propelling part of the electromagnetic trough has the advantage that the constant voltage device for eliminating fluctuations of the mains voltage need merely control that part of the induction coil that is associated with the delivery part of entire inductor voltage of the electromagnetic V conveyor trough. It is assumed that the voltage fluctuations in the mains supply are not sufficiently large enough to reduce the rate of flow of the liquid metal in the propelling part of the trough sufficiently for it to become less than that in the delivery part.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawing which shows a vertical section of a furnace and a schematically represented molten metal metering apparatus. I

As shown in the drawing, a holding or melting vessel 1 is provided with an upwardly inclined electromagnetic conveyor channel 2. The vessel 1 contains a body of molten metal 3 shown as having a level somewhat higher than the lower end of the channel 2 although the vessel 1 is capable of holding sufficient metal to bring the liquid level up to a higher point such as represented by the maximum level line max. Covers 4 and 5 are provided for the vessel 1 and the conveyor channel 2, respectively, to prevent radiation losses.

Moreover, the vessel 1 and the conveyor channel 2 are lined with a fireproof heat-insulating material. An inductor 7, shown schematically, is mounted directly under the conveyor channel 2. The necessary voltageto produce movement of the fluid metal is provided by a generator to which it is connected through a transformer 8, also shown schematically for simplicity, although the transformer and generator are actually three-phase devices. The inductor 7 comprises a three-phase winding which has a plurality of polar divisions or pole spans. For example, there may be eleven pole spans 20 as shown. The portion of the inductor winding at the upper end of the ninth pole span has a tap 10 connected thereto at a point above the highest of maximum bath level and the tap I0 is connected by means of a three-phase cable, shown schematically, to a connecting tap 12 of the transformer 8. In consequence, the main portion of the inductor winding between the lower end adjacent the vessel 6 and the tap 10 is energized with polyphase current when the three-phase main switch 14 of the generator 9 is closed.

In order to carry out the metering function, the remaining portion 18 of the inductor winding is adapted to be connected to the transformer 8 through another three-phase cable 13 by means of a three-phase on-olT switch 21. It will be understood that in actual practice, in a three-phase winding connections from the source of energy are made every 120 electrical degrees of spacing of the winding; but for simplicity, the threephase cable 13 is represented as being connected merely at the end. Likewise, in practice. there would be additional connections from the three-phase cables 1 l and 15.

The metering-of the molten metal takes place as follows. Normally the portion of the channel 2between the lower end and the point 17, which is above the maximum bath level. is energized with an electromagnetic field so that the liquid metal 3 rises to point 17 only. At point 17 there is a buildup of metal, and a certain quantity of the liquid metal is held at this point. From this point on, it will be observed that the remainder of the channel 2 is of a fixed length regardless of the level of the bath 3; then when a quantity of metal is to be delivered from the spout 19 into a suitable container or mold (not shown), the portion 18 of the winding is energized so that the metal has only a fixed distance to travel and a fixed quantity of metal will be delivered from the spout 19 within a given time. The quantity to be delivered is then controlled by controlling the length of time that the three-phase switch 21 is closed, which thus serves for metering the metal.

After the switch 14 is closed, the part of the inductor 16 which is tapped between the cable connections 15 and 11 receives voltage from the generator 9 through the transformer 8 so that the fluid metal 3 which has hitherto been stationary in the conveyor channel 2 is then set in motion and transported up to the tap position 10 of the inductor 7, which is the starting point 17 of the metering process for the liquid metal 3 in the conveyor channel 2. The liquid metal 3 remains at the starting point 17 as long as the inductor part 16 or preconveythe trough, so that it is less costly than if it were to control the ing part is'energized.

If a certain quantity of liquid metal 3 is to be delivered, the switch 21 is closed, whereby the upper apportioning portion 18 of the inductor is energized. The liquid metal 3, which is stationary at the starting point 17, then begins to flow up to the end of the conveyor channel 2 and pours over the nozzle 19 into a collecting vessel. Since the liquid metal 3 always traverses the same distance from the starting point 17 up to the end of the conveyor channel 2, the result is that the same quantity of liquid metal 3 is delivered from the conveyor channel 2 in the same time of pouring. By the continuous delivery of the liquid metal 3 by the voltage applied to the portion 16 of the inductor up to the starting point 17, which is always above the highest bath level, the metering process of the liquid metal can be practiced independently of the height of the bath level in the holding or melting vessel 1 and continues until the fluid metal remaining in the vessel is poured out. As mentioned above, the energy density of preconveying part 16 is -30 percent greater than in delivery portion 18. After the end of the metering process, the switch 21 is opened, whereby the portion 18 of the inductor becomes energized. In consequence, metal 3 in the channel 2 flows back and rests at the starting point 17 from which the next metering operation begins.

While the invention has been described as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that the invention if not limited thereto, since various modifications will suggest themselves to those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A method of conveying liquid metal in an electromagnetic conveyor trough having one portion of an electromagnetic coil associated with a liquid-propelling part of the said trough and another portion of the electromagnetic coil associated with a delivery part of the said trough, comprising controlling the energy density of the propelling portion of said coil so that it is from 10 to 30 percent higher than the energy density of the delivery portion of the said coil.

2. In the conveying of liquid metal in an electromagnetic conveyor trough with a sloping trough body wherein liquid metal in an open flow is conveyed up the trough and an inductor coil winding being divided into two successive portions, one portion associated with the preconveying part of said trough, while the succeeding portion, associated with the apportioning part at the delivery end of said trough and adapted to be energized only for the time metal delivery proceeds, the method of improving the accuracy with which the liquid metal is apportioned comprising controlling the energy density of the preconveying portion of the said coil, so that it is from 10 to 30 percent higher than the energy density of the apportioning portion of the said coil. 

2. In the conveying of liquid metal in an electromagnetic conveyor trough with a sloping trough body wherein liquid metal in an open flow is conveyed up the trough and an inductor coil winding being divided into two successive portions, one portion associated with the preconveying part of said trough, while the succeeding portion, associated with the apportioning part at the delivery end of said trough and adapted to be energized only for the time metal delivery proceeds, the method of improving the accuracy with which the liquid metal is apportioned comprising controlling the energy density of the preconveying portion of the said coil, so that it is from 10 to 30 percent higher than the energy density of the apportioning portion of the said coil. 